A conventional automatic fixed planting device for a hydroponic seedling is constituted by a seedbed conveyor that is rotated intermittently and caused to reciprocate to the left and right in order to convey a seedbed, a fixed planting panel conveyor that is disposed below the seedbed conveyor in parallel therewith and rotated intermittently in order to convey a fixed planting panel, a plurality of openable gripping conveyors positioned above a front end portion of the seedbed conveyor in order to respectively grip and separate a plurality of bed pieces on a front end row of the seedbed on the seedbed conveyor and convey the bed pieces forward, a plurality of openable gripping inserters positioned in front of the plurality of openable gripping conveyors in order to grip and lower the bed pieces conveyed by the openable gripping conveyors so that the bed pieces are inserted into holes in the fixed planting panel on the fixed planting panel conveyor and thus planted, and an operating mechanism that is connected to the seedbed conveyor to cause the seedbed conveyor to reciprocate intermittently in a left-right direction by the width of one bed piece of the seedbed at a time (see PTL 1, for example).